Caption: Milky Way and galaxies, illustration. The Milky Way (seen edge-on across centre) is the galaxy that contains our solar system. It is thought to be a barred spiral galaxy some 120,000 light years in diameter, containing as many as 400 billion stars. The inner bulge contains mostly older, redder stars, while the flat spiral arms contain younger, bluer stars and dusty nebulae. The Milky Way is one of billions of galaxies in the universe.